There is a color material which is decolorized when heated to a predetermined temperature or higher, and there is an image forming apparatus which performs printing on a sheet using this color material as a decolorable toner. In addition, there is a decolorizing apparatus which achieves reuse of a used sheet by heating the sheet to a predetermined temperature or higher. By the use of these apparatuses, it is possible to reduce environmental loads due to use of sheets.
A sheet deteriorates through repeated uses, but there is an image forming apparatus which manages accumulated deterioration of the sheet.
However, in a technique in the related art, a user cannot discriminate the deterioration extent of a sheet without using a specific instrument.